feat: initial commit — asaas-checkout template white-label

Template genérico de checkout com ASAAS, parametrizado via env vars.
Inclui fluxo completo: checkout → pedido → polling → webhook → admin.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/ui/calendar.tsx

@@ -0,0 +1,21 @@
+"use client"
+
+import * as React from "react"
+import { DayPicker } from "react-day-picker"
+import { cn } from "@/lib/utils"
+
+export type CalendarProps = React.ComponentProps<typeof DayPicker>
+
+function Calendar({ className, classNames, showOutsideDays = true, ...props }: CalendarProps) {
+  return (
+    <DayPicker
+      showOutsideDays={showOutsideDays}
+      className={cn("p-3", className)}
+      classNames={classNames}
+      {...props}
+    />
+  )
+}
+Calendar.displayName = "Calendar"
+
+export { Calendar }